The present invention relates to a distance measuring device of a camera for measuring a distance to a pictured object.
For an active type auto-focusing camera which is widely in use, there is provided only one beam projecting element, and the beam projecting element is pulse-driven responding to pushing on of a first step of a two-step release switch. When the number of light emission of the beam projecting element reaches a predetermined maximum number of light emission, 1,000 light emissions for example, or when an integrated value of an output of beam receiving means for receiving beam from the beam projecting element, reflected by a pictured object, reaches a predetermined value, pulse-drive of the beam projecting element is stopped. And, thereby a distance to the pictured object is recognized based on the output of the beam receiving means. When the distance to the pictured object is short, the received reflected beam is larger in quantity, so the integrated value of output of the beam receiving means reaches the predetermined value before the number of light emission of the beam projecting element reaches the maximum number of light emission. When the distance to the pictured object is long, the received reflected beam is small in quantity or becomes nil, so the beam projecting element is pulse-driven till the maximum number of light emission.
However, in the case of an auto-focusing camera like this, especially when measuring a distance to two pictured objects which are standing right and left with a space between them, an erroneous distance measurement results if the beam from the beam projecting element goes through the space between these two pictured objects.
From a viewpoint to avoid an erroneous distance measurement like this case, a distance measurement using multiple beams may be considered. In this measurement, there are provided three beam projecting elements for example, which are arranged in a row for projecting beams through the same projecting lens. There are generated three distance informations by pulse-driven these beam projecting elements one after another, and, a distance information with the smallest distance to give an example is selected out of these three distance informations. In such a measurement, however, when each of the beam projecting elements is pulse-driven to the maximum number of light emission because of a long distance to pictured objects, a time for the maximum number of light emission .times.3 is required, resulting in a long distance measuring time. Because of this, a time parallax between a release switch operation and a picture taking is increased, resulting in inability to take pictures with desired compositions, for example, of a moving object.